refactor(scripts): consolidate gate scripts on mdast fences, parseArgs, and globSync

Implements the gate-consolidation Agent Note from the NIH dependency audit:

- Shared markdownFences helper in scripts/markdown.ts (mdast code-node visit);
  doc-typecheck and verify-type-equiv extract fences through it; md-fences.ts
  and the duplicated extractEquivBlocks regex scanner are deleted;
  markdownProseLines derives fenced lines from parsed code-node positions
  instead of a second fence regex.
- publint-all.ts and verify-built-package-invariants.mjs parse argv with
  node:util parseArgs instead of hand-stepped parseOptions copies.
- Five straggler readdirSync walks become globSync: verify-runtime-closure,
  dev-web discoverPluginDirs, verify-package-paths realPackageNames,
  verify-client-domain-graph listSources, publint-all addPath. The
  dirent-diagnostic walks in check-workspace-constraints.ts and clean.ts stay.

Behavior parity verified: pnpm run doc-sync and every rewritten gate produce
byte-identical output before and after on this tree.

Moves the owning Agent Note proposed -> implemented and re-records its pair.

scripts/doc-typecheck.ts

@@ -10,7 +10,7 @@ import { globSync, mkdtempSync, readFileSync, rmSync, writeFileSync } from 'node
 import { join, relative, resolve } from 'node:path'
 import ts from 'typescript'
 import { builtDeclarationPath } from './doc-typecheck-paths.ts'
-import { extractFences } from './md-fences.ts'
+import { markdownFences } from './markdown.ts'
 import { partitionPairedMarkdownDerivatives } from './paired-markdown-derivatives.ts'
 
 const root = resolve(import.meta.dirname, '..')
@@ -45,8 +45,10 @@ const KIND_BY_INFO: Record<string, BlockKind> = {
 /** Extract every recognized TypeScript fence from one Markdown file. */
 function extractBlocks(absPath: string): Block[] {
   const file = relative(root, absPath)
-  return extractFences(absPath, info => KIND_BY_INFO[info] ?? null)
-    .map(f => ({ file, line: f.line, kind: f.kind, code: f.code }))
+  return markdownFences(readFileSync(absPath, 'utf8')).flatMap((fence) => {
+    const kind = KIND_BY_INFO[fence.info]
+    return kind === undefined ? [] : [{ file, line: fence.line, kind, code: fence.code }]
+  })
 }
 
 const configHost: ts.ParseConfigFileHost = {